1. Field of the Disclosure
The present disclosure relates generally to a method for processing an image acquired by means of a guide consisting of a plurality of optical fibers.
2. Description of the Related Art
Most systems for acquiring images with a fiber bundle image guide generally comprise a light source, a charge coupled device (“CCD”) detector and possibly a processing device for processing the acquired image. Other systems include a scanning device for scanning the proximal end of the fiber bundle, a receiver and a processing device for processing the acquired images. Image guides allow the CCD or the scanning device, the light source and the receiver to be shifted well away from the object which is to be observed. For example in a laser scanning system in which a confocal image is obtained, the image guide is an assembly of several thousand optical fibers whose spatial arrangement is identical at the entrance (generally referred to as proximal end) and at the exit (generally referred to as distal end).
Because of the loss of information due to the interstices between the optical fibers, processing of the acquired image and particularly image reconstruction is especially important. Indeed, the display is hampered because of the presence of the optical fibers pattern which appears on the acquired image. Patent application US2005/0207668 from the Applicant describes a process so as to eliminate this pattern and to take into account parasite effects by processing individually each zone of the acquired image associated with an optical fiber, Parasite effects arise from different causes, for example from Raman diffusion, from parasite reflections within the system, from fibers transmission heterogeneity, or in the case of fluorescence imaging, from fibers autofluorescence. In order to take into account parasite effects, patent application US2005/0207668 proposes a calibration process implemented through acquiring and processing several reference images in specific media. This process aims notably at determining calibration coefficients per fiber relative to each fiber specific properties.
Scanning of the bundle proximal end results at the distal end in a transposed scanning of an object under observation. As a consequence, the observed object emits light from the scanning which is transported via the fibers to a detector. Under certain conditions, for example low crosstalk and specific injection settings, the information content of each fiber does not depend on the neighboring fiber but only on the spatial coherence of the observed object. Each pixel of an acquired image corresponds to light stemming from the observed object transported via a determined fiber. Thus, it is possible to identify on an image groups of pixels associated to a fiber.
Determining per fiber calibration coefficients from reference images requires to associate pixels of a reference image to fibers of the bundle. This stage may, for example, be carried out by acquiring a reference image taken in a specific medium and by isolating on the image zones corresponding to each optical fiber. This geometrical detection of the fibers enables particularly to finely detect which fiber of a bundle is associated to a pixel of an acquired image.
Calibration relies on analyzing fiber per fiber response to acquired images in specific media and thereby depends on fibers geometrical detection. Calibration aims notably at compensating for defects independent from the imaged object properties. For example, in the case of fluorescence imaging, it allows compensating for defects arising from background fluorescence due to fibers autofluorescence. It enables also to take into account background noise due to parasite reflections in the optical system. Calibration aims also particularly at compensating for fibers physical characteristics heterogeneity, notably allowing determining injection and collection rates per fiber.
In certain applications, precision required for enabling accurate detection of an optical fiber in a bundle is inferior to a micrometer. Thus, any modification such as the replacement of a connector between the bundle and the scanning device, any unwanted displacement of the connector due to a shock or any modification with regard to the configuration in which the system has been calibrated may require renewing geometrical detection of the fibers and become cumbersome. Multiplying images acquisition for calibration purposes may be a burden for a medical specialist. Therefore, the present disclosure presents a new method and a related apparatus for processing an image acquired through a guide that overcome the aforementioned technical limitations.